1. Field of the Invention
The present invention relates to a liquid chromatograph including a high-speed liquid chromatograph and particularly to a liquid chromatograph including an autosampler for injecting a sample by a whole quantity injection system.
2. Description of the Related Art
Sample injection systems of the autosampler for the high-speed liquid chromatograph can be broadly divided into two systems, i.e., a loop injection system for injecting part of a sucked sample into an analytical flow path after filling it in a sample loop and a whole quantity injection system for injecting the whole quantity of a sucked sample into an analytical flow path as it is. The whole quantity injection system is a method by which the sample is less contaminated than by the loop injection system.
In the loop injection system, an injection needle is not connected to the sample loop, and the injection needle is connected to a sucking pump to suck and discharge the sample. To introduce the sample into the sample loop, the sample is sucked into the injection needle from a sample bottle with a sucking pump, and then the injection needle is connected to an injection port to introduce the sample in the injection needle into the sample loop from the injection port. A flow path is then switched over and the sample in the sample loop is introduced into a column with a mobile phase.
On the other hand, in the whole quantity injection system, an injection needle is connected to a sample loop. After a sample in a sample bottle is sucked into the sample loop through the injection needle, the injection needle is moved from the sample bottle to an injection port, a tip end portion of the injection needle is inserted into the injection port, the injection port and the injection needle are connected, and a flow path is switched over to introduce the sample in the sample loop from the injection needle into a column via the injection port by a mobile phase.
The injection port is made up of a needle seal having a through hole at its center and a nut for retaining the needle seal. The injection needle has a tapered tip end. With the tapered portion at the tip end of the needle fitted in the hole at the center of the needle seal, the injection needle inserted into the injection port is connected so that a solution does not leak.
The present invention relates to the whole quantity injection system out of the two sample injection systems. In the whole quantity injection system, the mobile phase used when the sample in the sample loop is introduced from the injection needle into the column via the injection port with the mobile phase is the mobile phase used for analysis in the column. A flow rate of the mobile phase at this time is a set flow rate of a solvent delivery pump for constantly sending the mobile phase out to the analytical flow path and is a certain flow rate determined in an original analysis condition.    Patent Document 1: Japanese Patent Application Laid-Open No. 2006-343271    Patent Document 2: Japanese Patent Application Laid-Open No. 5-256834    Patent Document 3: Japanese Patent Application Laid-Open No. 2003-215118
If the mobile phase is sent at the certain flow rate determined by the original analysis condition in introducing the sample in the sample loop from the injection needle into the column via the injection port with the mobile phase, the sample passes through a flow path joint section between the needle and the needle seal at high pressure. Although the tapered portion at the tip end of the needle and the hole at the center of the needle seal of the injection port are fitted with each other to achieve connection without the leakage of the solution, part of the sample may remain in a small clearance between the needle and the needle seal to contaminate this portion. If this contamination occurs, it affects carry-over performance of the autosampler for the high-speed liquid chromatograph.
The problem of the part of the sample remaining in the small clearance between the needle and the needle seal becomes more pronounced on an analysis condition of high solution sending pressure of the mobile phase, such as when a high-separation column having a particle diameter of packing material of 2 μm or smaller is used as a separation column of the analytical flow path.